(1) Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display, and more particularly, to an improved method for manufacturing a thin film transistor liquid crystal display, in which the number of photolithography processes to be performed is reduced.
(2) Description of the Related Art
A thin film transistor LCD (which is referred to as TFTLCD, hereinafter) which uses the thin film transistor as the active device has various advantages such as low power consumption, low voltage drive, a thin type, lightweight, etc.
Since the thin film transistor (TFT) is significantly thinner than a conventional transistor, the process of manufacturing the same is complicated, thus productivity thereof is low and manufacturing costs are high. In particular, since a mask is used in every manufacturing step, at least seven masks are required. Therefore, various methods for increasing productivity of the TFT and lowering the manufacturing costs have been studied. In particular, a method for reducing the number of the masks used during the manufacturing process has been widely researched.
FIGS. 1 to 4 are sectional views for explaining the method for manufacturing an LCD according to a conventional technology as disclosed in U.S. Pat. No. 5,054,887.
In the drawings, reference characters A and B denote a TFT area and pad area, respectively.
Referring to FIG. 1, after forming a first metal film by depositing pure Al on a transparent substrate 2, gate patterns 4 and 4a are formed by performing a first photolithography on the first metal film. The gate patterns are used as a gate electrode 4 in the TFT area and as a gate pad 4a in the pad area.
Referring to FIG. 2, after forming a photoresist pattern (not shown) which covers a portion of the pad area by performing a general photolithography, an anodized film 6 is formed by oxidizing the first metal film using the photoresist pattern as an anti-oxidation film. At this time, the anodized film 6 is formed on the entire surface of the gate electrode 4 formed in the TFT area and on a portion of the gate pad 4a in the pad area.
Referring to FIG. 3, an insulating film 8 is formed by depositing, for example, a nitride film on the entire surface of the substrate 2 having the anodized film. Then, after forming a semiconductor film by subsequently depositing an amorphous silicon film 10 and an amorphous silicon film 12 doped with impurities on the entire surface of the substrate 2 on which the insulating film 8 is formed, a semiconductor film pattern 10 and 12 to be used as an active portion is formed in the TFT area by performing a third photolithography on the semiconductor film.
Referring to FIG. 4, a photoresist pattern (not shown) is formed which exposes a portion of the gate pad 4a formed in the pad area by performing a fourth photolithography on the entire surface of the substrate 2 on which the semiconductor film pattern is formed. Then, a contact hole which exposes a portion of the gate pad 4a is formed by etching the insulating film 8 using the photoresist pattern as a mask. Then, a source electrode 14a and a drain electrode 14b are formed in the TFT area by depositing a Cr film on the entire surface of the substrate having the contact hole and performing a fifth photolithography on the Cr film. In the pad area, a pad electrode 14c connected to the gate pad 4a through the contact hole is formed. At this time, the impurity doped-amorphous silicon film 12 on the upper portion of the gate electrode 4 formed in the TFT area during the photolithography process is partially etched, thus exposing a portion of the amorphous silicon film 10.
Referring to FIG. 5, a protection film 16 is formed by depositing an oxide film, on the entire surface of the substrate 2 on which the source electrode 14a, the drain electrode 14b and the pad electrode 14c are formed. Then, the contact hole which exposes a portion of the drain electrode 14b of the TFT area and that of the pad electrode 14c of the pad area is formed by performing a sixth photolithography on the protection film.
Subsequently, pixel electrodes 18 and 18a are formed by depositing indium tin oxide ITO which is a transparent conductive material on the entire surface of the substrate having the contact hole and performing a seventh photolithography on the ITO film. As a result, the drain electrode 14b and the pixel electrode 18 are connected in the TFT area and the pad electrode 14c and the pixel electrode 18a are connected in the pad area.
According to the conventional method for manufacturing the LCD, pure Al is used as the gate electrode material for lowering the resistance of a gate line. Therefore, an anodizing process is required to prevent a hillock caused by the Al, thus complicating the manufacturing process, reducing productivity, and increasing manufacturing costs.